The present invention relates to an apparatus for measuring the amount of fuel remaining in a fuel tank of a motor vehicle equipped with an internal combustion engine, and more particularly to a remaining fuel amount measuring apparatus which is suited for the fuel tank designed to suppress generation of fuel vapor.
Generally, the motor vehicle equipped with an internal combustion engine includes a fuel tank. Reflecting the rising in consciousness of environmental conservation of earth in recent years, some fuel tanks have been proposed which are designed to suppress fuel vapor from dispersing into the atmosphere.
The fuel tank, as disclosed in Japanese Patent Unexamined Publication No. Sho 56-128221, includes an inside space of a tank body sectioned into a fuel chamber containing fuel and a pressure adjusting chamber communicating with the atmosphere by a shielding member so that the fuel stored in the fuel chamber is separated from contact with the atmosphere, thereby suppressing fuel vapor from generating.
The fuel tank generally includes a remaining fuel amount measuring apparatus for measuring the amount of fuel remaining in the tank. The above Japanese Patent Unexamined Publication No. sho 56-128221 describes an example of the application of a conventional remaining fuel amount measuring apparatus to a fuel tank designed to suppress the generation of fuel vapor. This remaining fuel amount measuring apparatus includes a shielding member which moves vertically in accordance with the vertical movement of a fuel liquid surface, a swinging rod which is provided with a roller in contact with the upper surface of the shielding member at the tip thereof and swings in accordance with the vertical movement of the fuel liquid surface as a fulcrum of a rod shaft provided on the upper side of the fuel tank. The fuel tank further includes a wiring resistor and a contact arm which is coupled with the swinging rod and slides on the wiring resistor at a fulcrum of the rod shaft. The remaining fuel amount measuring apparatus detects the position of the shielding member, i.e., fuel liquid surface in terms of an electric resistance of the wiring resistor. The detected liquid amount is indicated on a fuel meter located in a vehicle chamber so that a driver can know the remaining fuel amount by an indication on the fuel meter.
However, the above conventional remaining fuel amount measuring apparatus has a problem that the remaining fuel amount may be erroneously indicated on the fuel meter because of a change in a vehicle profile due to acceleration/deceleration and vibration of the vehicle, tilt of road, etc.
The reason is as follows. The surface of fuel liquid contained in the fuel tank largely swings in response to the change in the vehicle profile. This is attended with the vertical movement of the shielding member. Accordingly, the electric resistance of the wiring resistor indicative of the liquid amount changes.
In order to obviate such an inconvenience, some techniques of retarding the response of an indicator of a fuel meter have been proposed which include provision of a silicon damper with high viscosity at an indicator driving section of the fuel meter and of successively integrating the input electric resistance in converting the electric resistance into a remaining fuel amount to acquire the fuel amount on the basis of the integrated value of the electric resistance in a prescribed time.
However, retarding the response of the indicator of the fuel meter by using these techniques gives rise to a new problem of impairing the response of the indicator of the fuel meter, for example, a time is required for the indicator of the meter to indicate a correct indicated value at the time of full supply of fuel.
Further, the conventional remaining fuel amount measuring apparatus obtains an electric resistance which is a base of the measurement of the fuel amount by sliding a contact arm on a wiring resistance. However, poor contact between the wiring resistance and contact arm leads to an electric resistance not corresponding to a correct remaining fuel amount. This may make it impossible to measure the fuel amount at high accuracy for a long term.
The conventional remaining fuel amount measuring apparatus inherently having these plural problems is not preferably applied to the fuel tank designed to suppress the production of fuel vapor. Therefore, development of a new remaining fuel amount measuring apparatus suited to this kind of fuel tank has been demanded eagerly.